After I sent the post to all of you, I sent a second post to on of the
authors, Sherie Zahn. Her reply is below my signature line. The summary
is: we don't KNOW all that I think we KNOW.

I haven't changed anything in her post except to remove her email address.

Deb Beutler
Dept. of Zoology
Washington State University
Pullman, Whitman Co., WA

dbeutler at wsunix.wsu.edu
-----Original Message-----
From: Sherie Zahn
To: Deb Beutler <dbeutler at wsunix.wsu.edu>
Date: Tuesday, April 20, 1999 9:24 AM
Subject: Re: House Finch Plumage


>Dear Deb,
>
>I am gratified by the interest you have taken in my work, and by your
astute
>observations and questions. I shall reply to your major points, and you are
>welcomed to pass this on to the various list servers.
>
>
>>First, the data you report on the relationship between plumage color and
>>avian pox are correlational only. Of course, most of the studies on this
>>topic are correlational. Do you know if anyone is working on the causal
>>mechanism between the pox and pigment deposition? Has anyone fed two
>>groupsof males, one infected with pox and the other pox-free, the same
food
>>duringthe molt and measured the difference in plumage color?
>
>This is a very obvious experimental goal. However, it cannot work (or I
>would have done it). All male House FInches turn yellow if held in
captivity
>during the molt season - healthy ones, sick ones - all of them. Probably
due
>to the stress of confinement. Hill tried giving different concentrations of
>carotenoids to healthy captive males, and found that he could indeed
>manipulate plumage color this way. I question the real value of this, since
>I could manipulate your skin color by feeding you an all-carrot diet, but
>what would this really say about your metabolism or state of health? And
the
>death rate of captive sick birds is very high (Power, D. M., and G. Human.
>1976. A local occurrence of avian pox in the House Finch. Condor
>78:262-263.)
>
>
>
>>Second, you acknowledge that the shift from red to orange-yellow plumage
>>occurs around the time of increased dependence on human food rather than
>>natural food. You use this as evidence that the plumage-color shift is
>>related to avian pox because the feeders increase the transmission of the
>>disease. The data from the eastern U.S. also supports this idea.
However,
>>has anyone really tested this?
>
>It is highly unlikely that many, if any, wild birds use feeders
exclusively.
>Even at my regular feeding stations, I did not see the same birds there all
>or even most of the time. There were some who came more often than others,
>but House Finches have broad ranges.
>
>
>You also ask, "Does a human diet of sunflower seed provide
>>sufficient carotenoids to make bright red plumage? Has anyone done an
>>aviary study on this?"
>In your list server message you state "It is generally assumed that yellow
>House >Finches eat a diet that is low in
>>carotenoids and the red House Finches eat a diet high in
>carotenoids....>What we >do know is birds do not "make" the pigment,
>carotenoids, that cause
>>the red to yellow colors in feathers. They have to get these chemicals
>>from their diets.
>
>Whoops - lots of misconceptions here. There has been work done by Stradi
>(Stradi, R., G. Celentano, E. Rossi, G. Rovati, and M. Pastore. 1995.
>Carotenoids in bird plumage - I. The carotenoid pattern in a series of
>Palearctic Cardulinae. Comparative Biochemistry and Physiology
>110B:131-143.) and now probably by Inyoue , demonstrating that the
>carotenoids found in the House Finch red pigment are not present in ANY of
>the dietary components, the probability being that they use ingested
>carotenoids as precursors from which they are able to metabolize other
>molecular configurations. House Finches are flock feeders - they all eat
the
>same thing. There is not a shred of evidence to the contrary.
>
>
>>redder males are dominant over yellow males and will sire offspring at are
>>higher in status than yellow males. Or the red males are better at
getting
>>food than the yellow males and will make better providers."
>
>Red males are NOT dominant over yellow males. READ:
>Belthoff, J. R. and S. A. Gauthreaux Jr. 1991. Aggression and dominance in
>House Finches. Condor 93: 1010-1013.
>
>Belthoff, J. R., A. M. Dufty Jr., and S. A. Gauthreaux Jr. 1994. Plumage
>variation, plasma steroids and social dominance in male House Finches.
>Condor 96: 614-625.
>
>Belthoff, J. R. and P. A. Gowaty. 1996. Male plumage coloration affects
>dominance and aggression in female House Finches. Bird Behavior, Vol. 11:
>1-7.
>
>Brown, M. B. and C. R. Brown. 1988. Access to winter food resources by
>bright - versus dull-colored House Finches. Condor 90: 729-731.
>
>Zahn, unpublished data).
>
>Your second statement is based on a very weak paper by Hill in which red
>males made more trips to the nest. But red males have been found to be
>subordinate to or at best equal to, yellow males - perhaps they had to make
>more trips because they could only get lower quality food. I don't really
>believe that, either. Frankly, I spent 6 years observing House Finches - I
>believe that all color males provide equally well.
>
>
>>Therefore, the red color is "signal of status" to female House Finches...
>We also know that female House Finches prefer to mate with
>>red males over orange or yellow males.
>
>Be very careful about what you claim to be "known". Hill has performed
>experiments that appear to demonstrate female preference for red males. I
>have performed mate choice studies, eliminating some of the confounds
>present in Hills design, and have found that individual females have
>different color preferences, and that those preferences are consistent on
an
>individual basis. Some preferred red, some orange, some yellow -
repeatably.
>This paper is being prepared for publication. I hypothesize that they may
be
>imprinting on their fathers, who would have served as a logical model for a
>good male provider.
>
>>Finally, my biggest problem with the whole idea is the delay between the
>>molt (October) and the female selecting males (in spring). Doesn't it
seem
>>odd that females would use a signal that could be giving false results? A
>>male that was sick in October and molted into yellow feathers might be
>>perfectly healthy in the spring while a male that was healthy in October
>and
>>molted in to bright red feathers might have pox right now and could give
it
>>to her and her offspring. Doesn't that seem like a poor indicator? The
>>plumage color would only work as an indicator of male fitness if a
>>resistance to avian pox is genetic and could be passed to the offspring.
>>Has that been tested?
>
>I agree with your evaluation of the mate choice dilemma. But you make the
>assumption that females prefer red males, which well may be an incorrect
>premise.
>
> We also know the color differences are
>>not related to genetic factors: yellow male can molt into red males and
>>vice versa.
>
>You KNOW that genetics is not involved? Better read up on phenotypic
>plasticity. Genetics is everything....
>
>
>Hope this has been helpful.
>
>Best,
>
>Sherie Zahn
>